In ink-jet recording methods, a fine droplet of ink is ejected by various principles to adhere onto a recording sheet to record an image or a character. This method has advantages such as relative high speed recording, low noise and easy multi-color recording.
Recently, the ability of printers to produce a high quality image has progressed and the image quality approaches that of photographic images. Accordingly, it is desired for recording sheets to equal the image quality of conventional photographs and to reproduce the feeling of silver halide photographs such as glossiness, smoothness and stiffness.
Known as a method for reproducing the feeling of silver halide photographs is the use of so called swelling type ink receiving sheet which is constituted of a support and a hydrophilic binder layer such as gelatin and poly(vinyl alcohol) coated onto the support. However, a method has drawbacks such that the ink absorbing speed being too slow, the surface after recording tends to be sticky and the image easily bleeds during storage under high humidity. Specifically, bleeding between different colors and bleading of the same color caused by the mixing of ink droplets before absorption of the ink tend to occur since the absorption speed of the ink is slow. Consequently, the image quality of the silver halide photograph is very difficult to be attained.
High glossiness and suitable ink absorption can be attained by the combination of an aqueous dye ink and a porous type ink receiving sheet, and image quality approaches the level of photographs.
In addition, the storage stability of the ink-jet image compares favorably with that of usual photographs, accompanied with the improvement of quality of images produced by ink-jet recording. In such situations, it is pointed out, particularly in the case of aqueous dye ink, that the degradation caused by migration of the colorant due to weak resistivity to water and bleeding, and degradation caused by chemical reaction of colorants such as low light fastness and resistivity to oxidants.
Various trials have been performed to attain the image quality of ink-jet recorded images to the level of silver halide photographs. Examples of technology for improving low light fastness are disclosed in Japanese Patent Publications Open to Public Inspection, hereinafter referred to as JP-A, 57-74192, 57-87989, 57-74193, 58-152072, 64-36479, 1-95091, 1-115677, 3-13376, 4-7189, 7-195824, 8-25796, 11-321090, 11-277893 and 2000-37951.
In the case of porous type ink receiving sheets, one problem is discoloration of images caused by toxic gases, such as oxidant gas tends to be produced due to the porous structure. Such problem often occurs with phthalocyanine type water-soluble dye which is used in typical color ink-jet printers.
It is assumed that the discoloration is caused by the oxidation of the dye by a slight amount of reactive toxic gases in ambient air such as ozone, SOx, NOx, and other oxidants since the fine porous structure has a large surface area and the inorganic fine particles used in the porous structure has an active surface. However, the mechanism of this discoloration is not yet confirmed.
Technologies for improving the discoloration are disclosed, for example, in JP-A63-252780, 64-11877, 1-108083, 1-216881, 1-218882, 1-258980, 2-188287, 7-237248, 7-266689 and 8-164664. However, the effects of the known technology are insufficient in the ink receiving sheet to achieve photographic quality images having a still more fine porous structure. Accordingly, more drastic improvement is demanded.
A method of adding film resin particles into the water-soluble dye ink is known as one of the methods for minimizing discoloration. However, it has been found that color bleeding of the ink tends to occur when the image is printed onto ink receiving sheets having the porous ink receiving layer by ink containing latex. It is assumed that the color bleeding occurs due to the latex contained in the ink closing the pores on the surface of the porous type ink receiving layer in the course of absorption of the ink into the ink receiving layer, whereby the ink absorbing ability of the ink receiving sheet is lowered.
The glossiness of the surface of the ink receiving layer is an important factor in forming a bright color image when a photograph like image is formed via the ink-jet recording methods. The glossiness of the image is lowered and the brightness of the color is degraded when an ink containing latex is used, even if the glossiness of the surface of the ink receiving layer is high.